Loans and Card Member Receivables - Modifications Subsequently Defaulted (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	$ 83	$ 74	$ 114	$ 103
Interest Rate Reduction and Term Extension
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	2	1	2	2
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	66	57	91	80
Term Extension
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	15	16	21	21
Card Member Loans | Consumer
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	45	40	62	56
Card Member Loans | Small Business
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	21	17	29	24
Card Member Loans | Corporate
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Loans | Interest Rate Reduction and Term Extension | Consumer
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Loans | Interest Rate Reduction and Term Extension | Small Business
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Loans | Interest Rate Reduction and Term Extension | Corporate
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Loans | Interest Rate Reduction | Consumer
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	45	40	62	56
Card Member Loans | Interest Rate Reduction | Small Business
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	21	17	29	24
Card Member Loans | Interest Rate Reduction | Corporate
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Receivables | Consumer
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	5	5	6	6
Card Member Receivables | Small Business
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	9	11	14	15
Card Member Receivables | Corporate
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	1	0	1	0
Card Member Receivables | Interest Rate Reduction and Term Extension | Consumer
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Receivables | Interest Rate Reduction and Term Extension | Small Business
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Receivables | Interest Rate Reduction and Term Extension | Corporate
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Card Member Receivables | Term Extension | Consumer
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	5	5	6	6
Card Member Receivables | Term Extension | Small Business
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	9	11	14	15
Card Member Receivables | Term Extension | Corporate
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	1	0	1	0
Other Loans
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	2	1	2	2
Other Loans | Interest Rate Reduction and Term Extension
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	2	1	2	2
Other Loans | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	0	0	0	0
Other Loans | Term Extension
Financing Receivable, Modifications [Line Items]
Account balance, modified and subsequent default	$ 0	$ 0	$ 0	$ 0